The date is coded as a 1- or 2-digit month and a single letter week.
Some plants would pad a single digit month with a leading zero (0), some
did not.

Number

Month

Number

Month

01

January

07

July

02

February

08

August

03

March

09

September

04

April

10

October

05

May

11

November

06

June

12

December

Week Letter A through E

The week letter typically ranges from A to D and an occasional week letter
E has been found. The letter "A" is the first week, the letter "B" is
the second week, etc. However, there is not a direct correlation between
a week letter and specific days or a physical week of any given month
and each plant seemed to have their own standard operating procedures
explaining why some plants for a given month may have the letter "E" for
a fifth week when other plants do not for that month.